Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753315AbdHKPb5 (ORCPT ); Fri, 11 Aug 2017 11:31:57 -0400 Received: from mx2.suse.de ([195.135.220.15]:39322 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752869AbdHKPbz (ORCPT ); Fri, 11 Aug 2017 11:31:55 -0400 Date: Fri, 11 Aug 2017 17:31:52 +0200 From: Michal Hocko To: Florian Weimer Cc: Colm =?iso-8859-1?Q?MacC=E1rthaigh?= , Kees Cook , Mike Kravetz , Rik van Riel , Will Drewry , akpm@linux-foundation.org, dave.hansen@intel.com, kirill@shutemov.name, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, luto@amacapital.net, mingo@kernel.org Subject: Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK Message-ID: <20170811153152.GR30811@dhcp22.suse.cz> References: <20170810130531.GS23863@dhcp22.suse.cz> <20170810153639.GB23863@dhcp22.suse.cz> <20170810170144.GA987@dhcp22.suse.cz> <20170811140653.GO30811@dhcp22.suse.cz> <20170811142457.GP30811@dhcp22.suse.cz> <6a04f59b-b72b-c468-ea5c-230764a24402@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6a04f59b-b72b-c468-ea5c-230764a24402@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2051 Lines: 42 On Fri 11-08-17 17:24:29, Florian Weimer wrote: > On 08/11/2017 04:24 PM, Michal Hocko wrote: > > On Fri 11-08-17 16:11:44, Florian Weimer wrote: > >> On 08/11/2017 04:06 PM, Michal Hocko wrote: > >> > >>> I am sorry to look too insisting here (I have still hard time to reconcile > >>> myself with the madvise (ab)use) but if we in fact want minherit like > >>> interface why don't we simply add minherit and make the code which wants > >>> to use that interface easier to port? Is the only reason that hooking > >>> into madvise is less code? If yes is that a sufficient reason to justify > >>> the (ab)use of madvise? If there is a general consensus on that part I > >>> will shut up and won't object anymore. Arguably MADV_DONTFORK would fit > >>> into minherit API better as well. > >> > >> It does, OpenBSD calls it MAP_INHERIT_NONE. > >> > >> Could you implement MAP_INHERIT_COPY and MAP_INHERIT_SHARE as well? Or > >> is changing from MAP_SHARED to MAP_PRIVATE and back impossible? > > > > I haven't explored those two very much. Their semantic seems rather > > awkward, especially map_inherit_share one. I guess MAP_INHERIT_COPY > > would be doable. Do we have to support all modes or a missing support > > would disqualify the syscall completely? > > I think it would be a bit awkward if we implemented MAP_INHERIT_ZERO and > it would not turn a shared mapping into a private mapping in the child, > or would not work on shared mappings at all, or deviate in any way from > the OpenBSD implementation. If we go with minherit API then I think we should adhere with the BSD semantic and alloc MAP_INHERIT_ZERO for shared mappings as well > MAP_INHERIT_SHARE for a MAP_PRIVATE mapping which has been modified is a > bit bizarre, and I don't know how OpenBSD implements any of this. It > could well be that the exact behavior implemented in OpenBSD is a poor > fit for the Linux VM implementation. yeah, it would be MAP_INHERIT_SHARE that I would consider problematic and rather go with ENOSUPP or even EINVAL. -- Michal Hocko SUSE Labs